Dissociation of Liquid Water on Defective Rutile TiO2 (110) Surfaces Using Ab-Initio Molecular Dynamics Simulations

TL;DR

This study uses ab initio molecular dynamics to explore how water interacts with perfect and defective rutile TiO2 (110) surfaces, revealing that certain defects influence water dissociation rates contrary to previous assumptions.

Contribution

It provides new insights into the thermodynamics and kinetics of water dissociation on TiO2 surfaces, especially regarding the role of oxygen vacancies.

Findings

Water dissociation has a high free-energy barrier (~4.4 kcal/mol) on perfect TiO2 (110).

Unstable oxygen vacancies promote water dissociation, while the most stable Vo1 does not.

Water dissociation is exothermic and enhances TiO2's hydrophilicity.

Abstract

In order to obtain a comprehensive understanding of both thermodynamics and kinetics of water dissociation on TiO2, the reactions between liquid water and perfect and defective rutile TiO2 (110) surfaces were investigated using ab initio molecular dynamics simulations. The results showed that the free-energy barrier (~ 4.4 kcal/mol) is too high for a spontaneous dissociation of water on the perfect rutile (110) surface at a low temperature. The most stable oxygen vacancy (Vo1) on the rutile (110) surface cannot promote the dissociation of water, while other unstable oxygen vacancies can significantly enhance the water dissociation rate. This is opposite to the general understanding that Vo1 defects are active sites for water dissociation. Furthermore, we reveal that water dissociation is an exothermic reaction, which demonstrates that the dissociated state of the adsorbed water is thermodynamically favorable for both perfect and defective rutile (110) surfaces. The dissociation adsorption of water can also increase the hydrophilicity of TiO2.